Some Europeans have enhancers that make them blond. In this case, the enhancer isn’t a hair dye, but a genetic variation that controls pigment production in hair follicles, David Kingsley, an evolutionary geneticist at Stanford University and colleagues report June 1 in Nature Genetics.

Previous studies had indicated that a genetic variant known as a single nucleotide polymorphism, or SNP, is associated with blond hair in Europeans. Why the variant affects hair color wasn’t clear because it is not part of a gene. Now Kingsley’s team provides evidence that the blond-inducing variant lies within a piece of DNA known as an enhancer. Enhancers are stretches of DNA typically located far from genes that nevertheless help control gene activity.

Kingsley’s team genetically engineered mice to carry the SNP and found that they developed lighter colored coats than did mice with the non-blond version of the enhancer.

The enhancer helps control activity of a gene already known to be involved in pigment production. This blond version of the enhancer turns down gene activity in hair follicles, leading to lighter colored hair, but it doesn’t affect eye or skin pigmentation, the team found.